Switch device for point selector electrodes in flat television screens

ABSTRACT

This invention provides a switching device for point selector electrodes in flat television screens comprising horizontal and vertical electrodes, able to vary progressively the potential of said electrodes in order to scan an image, characterized in comprising an electron emissive cathode with focusing electrodes able to obtain an electron beam having a cross-section at least 10 times longer than wide; at least one electrical resistance in the shape of an elongated bar having a length at least equal to that of said focusing electrodes and arranged parallel to the outlet opening (of the electron beam) provided on the said electrodes.

United States Patent 1191 Sullos SWITCH DEVICE FOR POINT SELECTORELECTRODES IN FLAT TELEVISION SCREENS Inventor:

[76] Ludwig Sullos, Acevedo 1439,

Banfield, Buenos Aires, Argentina Filed: Feb. 12, 1973 Appl. No.:331,443

[30] Foreign Application Priority Data Feb. 17, 1972 Argentina 240578U.S. Cl 313/422, 313/432,-313/105 Field of Search 313/82 NC, 78; 315/3References Cited UNITED STATES PATENTS 11/1939 Barthelemy.. 315/8 9/1948SZiklai 313/78 X Int. Cl H0lj 29/74, HOlj 29/56 1 Dec. 3, 1974 6/1959Van Doorn et 111...... 3l3/78 x 5/1973 Buck 315/3 PrimaryExaminer-Robert Segal Attorney, Agent, or FirmLadas, Parry, Von Gehr,Goldsmith & Deschamps [5 7] ABSTRACT 5 arranged parallel to the outletopening (of the electron beam) provided on the said electrodes.

2 Claims, 2 Drawing Figures PATENTEL BEE 3 74 SWITCH DEVICE FOR POINTSELECTOR ELECTRODES IN FLAT TELEVISION SCREENS This invention is relatedto a deflection device for flat imaging screens. More particularly, itis related to flat television screens comprising a flat photocathode ofa size similar to that of the image; a control grid system printed on apolyethylene body operating as point selectors horizontallyv andvertically arranged grids and color selectors, the latter being able toproduce a postdeflection and to cause the current controlled thereby toactivate a colored mosaic conveniently provided for obtaining the threeprimary colors. To return to the point selector grids, the instantdevice is applicable to energizing said grids in series and at a speedrequired by the vertical and horizontal scanning sweepings. v

Similar devices are known which operate using a photocathode andsecondary emission multiplier electrodes; they operate so that each gridhas an associated circuit providing the voltage changes required by saidgrid and causing that when a grid returns to an unenergized condition,the following grid is energized. This is achieved by means of resistorsand capacitors coupling the circuit of one grid to the following.Moreover, the return of a grid to an unenerg ized condition and theenergization of the following grid are controlled by an external circuitan oscillator assuring the uniformity of the energization intervals.Such devices assure an excellent linearity, but their principal drawbackis caused by the complexity in the production of the coupling circuitbetween the grids, inasmuch as if there are 700 grids, the same numberof coupling circuits is required, and each of them may comprise acondensor and various resistances and. including control electrodes onthe photocathode portion corresponding to the same or the adjacent grid.

The instant device eliminates all the coupling elements between adjacentgrids and as willbe seen later reduces considerably the production costof the flat screen while increasing its operational stability.

FIG. I is a sectional view through a bar in which the point selectorgrids terminate, and FIG. 2, in its top portion, shows the selectorgrids as a grate with the respectivebars wherein they begin andterminate. The bottom portion of FIG. 2 is an operational graph whichshall be explained later. It is to be assumed that the grate is arrangedover an extended photocathode surface (not shown) without touching it,so as to be able to control the current emitted by said surface. In thiscase, if all the grids are negative 10 volts with respect to thephotocathode, no current passes through the grating. If a pair of grids,perpendicular to each other, become positive or at zero potential withregard to the photocathode, and if a positive electrode ,(not shown) isprovided on the opposite side, there will The energization of each gridis achieved as'follows: the grids are dipped at one of their ends inresistive paste which is represented in FIG. 2 by details 19 and 25, andin such a way that each grid receive a 10 Kohm resistance with a commonelectrode. The other ends of the grids terminate in detail 18 of FIG. 2constituted by respective tabs each with a-surface prepared so as tohave a high secondary emission for changing the potential of theassociated grid in response to electron beam impingement of the surface.One of these surfaces is illustrated in FIG. 1 at 9, with 14 being thereference number of the polyethylene body serving as its base. Thiselectrode is energized by V electrons and an efficiency factor 4emission is produced; the energizing current is l mA and the emittedcurrent is 4 mA, meaning that for the 10 Kohm resistorof thecorresponding grid 3 mA will circulate and cause the potential of saidgrid to vary towards a more positive value. This effect should beachieved in such a way that theenergizing area be transferred from tabto tab at the required speed. In FIG. 2, 15, 16 and 17 constitute thedevice used to achieve this end. 15 is a photocathode and a focusingsystem producing a long and narrow electron ing the same length isprovided for dissipating the heat generated by resistance 5. Number 17in FIG. 2 indicates the electron multiplying system which in FIG. 1

is represented in perpendicular section by elements 7, jointly withelement 8 which is the'terminal collector anode, shaped as a thickcopper bar the purpose of which is to dissipate the heat. FIG. 1 is asection through the deflection device at any point of a perpendicularplane,except details 9 and 14 which pertain to the plastic sheetcarrying the point selector grids. This device is comprised solely byparallel bars, mounted in plastic 13 and does not contain specificdetails corresponding to individual grids. Number 10 is aphotocathodesurface, and 11 is a luminous phosphor coated electrode constituting aregenerative photocell, with the sole purpose of illuminatingphotocathode 1 with a light having a given value in the order of 1000lux inasmuch as the electron emission from 1, on its entire surface,should not be in excess of 60 uA. Electrode'2 has the same potentialasl, electrode 3 has a potential in the order of 5 20 V; 4 is a focusingelectrode adjustable for obtaining the narrowest possible beam. 5 is along resistor, made of a paste very uniform as to its resistivecharacteristics, the purpose of which is to deflect the beam as obtainedto one side or the other, enabling the electrons to enter the multiplierenclosure only in the area where said resistor has the same potential aselectrode 3; this resistor, whose input terminals are 26 and 27 FIG. 2has an end to end or terminal to terminal value of 250 -.800 Kohm tominimize the current flow therein; the values comprised between the saidextremes are optimal. Electrode 6, at a potential in the order of 40 200V is a beam director permitting the electrons to arrive at the mostappropriate portion of 7; 7 is a secondary emission multiplier electrodethe same as the remaining similarly shaped electrodes following in line.In the experimental tests pitches of 300 or 400 V were used in order toobtain factors in the order of the 6s and to cause the last electrode 7to emit 1 mA.

The operation is simple. In the first tests, resistor S was at 500 Kohmand between terminals 26 and 27 350 V were applied. Thereafter, byenergizing both ends with a saw-tooth voltage, the transfer of the pointwhere the potential of resistor is equal to that of focusing electrode 3was achieved, and therewith the transfer of a narrow beam energizingsurfaces 9 of the tabs 18. The bottom portion of FIG. 2 is adiagrammatic illustration of the voltages appearing on resistance 5. Theenergization of said resistance must be such as to provide at any time avoltage of 350 V between its ends. For instance, on line 21, at the leftend the voltage is zero and at the right end, 350 volt. Straight line 22shows what happens when all the points of resistance 5 vary by 200 volt;it is noted that although the voltage distribution has not varied withregard to the ends, it has varied with regard to the zero volt line.This is achieved by applying the same voltage variations to both ends ofresistance 5. The other extreme position is the one shown on line 23,where the left end is at 350 volt and the right end at zero volt.Between the conditions illustrated by 21 and 23, it is possible to passthrough all the intermediate positions, i.e., by causing the points ofthe lines to correspond with the points of resistor 5, it is possiblefor each point to pass at a given moment through the zero volt line. Ifsaid line is the one representing the potential of electrode 3 and ifboth ends of resistor 5 are energized with the same saw-tooth voltage,the point at zero volt will sweep during each cycle the entire resistor.On the other hand, zero volt point is where the beam formed byelectrodes 1, 2, 3 and 4 may enter the hole in electrode 3 and reach thesecondary emission electrodes. The width of the entering beam is thesmaller, the larger is the continuous potential between the terminals of5. With 350 V a width below 1 mm was obtained. The current reaching themultiplier electrodes is in the order of 0.1 microamper; it varieswiththe variation of the focusing electrodes, however it is possible toobtain it as narrow as the minimum detail of the image on the screen. Inpractice, a drawback was encountered: for instance, inthe case of line22, the entire portion of 5 which is at a positive potential with regardto 3 absorbs the current emitted by photocathode 1, while the remainingportion does not absorb beam current, repel ling the beam so as to beabsorbed by electrode 3. This current absorbed by 3 produces adeformation of the linearity, inasmuch as it alters the potentials of 5by displacing the zero volt point. Said current is in the order of 60p.A. With 5 at 500 Kohm and 350 V between the terminals, the continuouscurrent by 5 is of 700 uA. This means that the 60 [LA constitute lessthan percent of the total, thus causing a nonlinearity in the sameorder. In practice, this drawback has been solved by altering the shapeof the sawtooth wave energizing both terminals of 5; by means ofR-C-circuits, a linearity in the order of 2 percent was achieved at thefirst try; i.e., the disturbing effect of the current absorbed by 5 canbe obviated by circuit arrangements outside the screen. Copper bar 12became unnecessary, inasmuch as the heat dissipation of 5 amounted to250 mW. And as the physical dimensions of 5 were those of an 8 X 8 mm by500 mm length bar, the heating was negligible. As to the tab 18, theheat dissipation may pose a problem if the sweeping were detained at anintermediate point of the screen. The last secondary emission multiplierelectrode 7 emits l mA. Tab 18 in FIG. 2, and surface 9 in FIG. 1 are at120 V with regard to the above mentioned electrode and through secondaryemission emits 4 mA which are absorbed by electrode 8 which is at 50 100V with regard to 9. 8 is a thick copper bar and obviates the heatingproblem, inasmuch as it must dissipate merely 400 mW. However, surface 9is a plate 0,7 mm wide not more than 6 mm long. The remainder penetratesinto the screen acting as a point selector. The plate receiving 1 mA atl20 V, that is having to dissipate l2O mW, becomes very hot if the beamis detained; in practical experience, the assembly of sur faces 9,totalling 300 surfaces, each having a width of 1 mm, was mounted in theform of a circuit printed on a phenol-formaldehyde plastic materialreinforced with amiantus fiber which was appropriately positioned withregard to electrode 8. We shall refrain from describing the manner inwhich the dynamic voltages on each surface 9 were taken, as such adescription would be very extensive and unrelated to the main object ofthis patent. The plastic material did not vary with I20 mW, however dueto the impurities existing between the copper and its base, as thecurrent and the dissipation increased, the sheet peeled away from itsbase and the appearance of gases made a repetition of the high vacuumprocedure necessary. In another experience, the tabs were mounted on athick copper bar, separated by a 0.2 mm thick chemically settableadhesive layer; in this new arrangement the heating problem was solved.This means that if due to a breakdown of the deflection voltagegenerator the energized point were detained, the screen would notdeteriorate. Another reason for nonlinearity which appeared withsawteeth in excess of l0 Kc/sec was the capacity distributed byresistance 5. This was obviated with an appropriate modification of thesaw-tooth exciter through R-C loops. For frequencies of 50 cycles persecond the distributed capacity posed no problems. For the illuminationof photocathode 1 an arrangement of elements already described see FIG.1 was used, based on a regenerative photocell. Photocathode 10 emitselectrons and surface 11 is a transparent conductor coated with type P4phosphor. Due to deficiencies in the deposition, the critical voltagewas in the order of 4 KV. The current was limited by means of aresistance in series; by regulating the value of said resistance it waspossible to vary the light energizing the photocathode l and itsemission, limiting the same to uA as total current. In a later test, bythe application of 600 V pitches between multiplier electrodes, anemission of 1 mA was achieved in the last electrode 7, with a totalemission from photocathode 1 not in excess of IO A; with the latter, itwas possible to obviate the circuit for the correction of linearitythrough absorption of the current from resistor 5, inasmuch as thenonlinearity produced by the absorbed current is as low as 1.4 percentat the edge of the screen.

FIG. 2 is a diagrammatic illustration of a point selector device with amatrix of horizontal and vertical grids. Detail 20 corresponds to thebeam generating focusing, deflecting and electron multiplying devicesassociated with tabs 18 and the vertical grids; 24 are the correspondingtabs, fulfilling the same purpose as tabs 18; 25 is the compact bar ofresistive paste in which terminate the horizontal grids. Neither theflat luminescent imaging screen not the flat photoemissive surface Iwhose emitted electrons may be controlled by the matrix to impinge pointby point on the screen are shown;

To resume, it is stressed that in the flat screen with 600 horizontaland 700 vertical grids, measuring 36 X 47 cm, there is a total of1,300,000 points as each grid is able to control two image points whichis by far in excess of the present requirements of television. Thereduction in the number of grids there can be 300 and 350 simplifies theproduction. The color selector plates, which are applicable to thescreen as described and which are comprised of deflector grids andmultiplier plates, allow the obtention of flat color television screenscompatible with systems of up to 400,000 points, the production costbeing in the long run very similar to that of the present black andwhitereceivers, but of a quality indisputably superior to that of any of theknown color systems.

Having thus described and determined the nature and scope of the'presentinvention and the manner in which the same is to be put into practice,it is hereby stated that what is claimed as invention and exclusiveproperty is: e

l; Deflection apparatus for flat imaging screens, comprising incombination:

a. a cathode and focusing electrodes for generating a flat electron beamhaving a width substantially equal to that of the image to be produced,two deflecting electrodes positioned on opposite sides of the path ofsaid flat beam and in parallel relationship to said focusing electrodes,one of said deflecting electrodes being of resistive material andhavhaving a slit parallel to said deflecting electrodes;

b. multiplier electrodes having a length substantially the same as thatof said deflecting electrodes and being disposed in parallelrelationship to said slit, said multiplier electrodes being followed bya terminal collector anode of the same length;

c. a row of tabs disposed in parallel relationship to said multiplierelectrodes and having respective secondary emission surfaces in positionbe be impinged successively by said flat electron beam as the beam isnarrowed and undergoes deflection in the direction of said row under theinfluence of said deflecting electrodes, each tab being electricallyconnected to one end of a respective one of a plurality of image controlgrids arranged in a common planewithout touching each other and lyingperpendicular to said row, the opposite ends of said image control gridsbeing coupled by way of resistive means to a common terminal; and,

. a duplication of (a), (b) and (c) wherein the common planes of the twopluralities of image control grids are adjacent and parallel, with saidpluralities being mutually perpendicular to form a matrix of imagecontrol grids, said matrix beingadapted to be disposed in non-contactingrelationship to and between transparent photoluminescent andphotoemissive plane parallel surfaces equal in size to that of the imageto be produced so as to control the impingement of electrons emittedfrom the photoemissive surface upon the photoluminescent surface. v

2, Apparatus according to claim 1, wherein said terminal collector anodeis a metal bar electrically insulated from said tabs and positioned todissipate heat developed in said tabsby impingement of the. electronbeam thereon.

1. Deflection apparatus for flat imaging screens, comprising incombination: a. a cathode and focusing electrodes for generating a flatelectron beam having a width substantially equal to that of the image tobe produced, two deflecting electrodes positioned on opposite sides ofthe path of said flat beam and in parallel relationship to said focusingelectrodes, one of said deflecting electrodes being of resistivematerial and having two terminals by which current may be appliedthrough said one deflecting electrode to flow in a directionperpendicular to the electron flow in said flat electron beam, and anelectrode disposed in parallel relationship to said deflectingelectrodes on the side thereof remote from said cathode and having aslit parallel to said deflecting electrodes; b. multiplier electrodeshaving a length substantially the same as that of said deflectingelectrodes and being disposed in parallel relationship to said slit,said multiplier electrodes being followed by a terminal collector anodeof the same length; c. a row of tabs disposed in parallel relationshipto said multiplier electrodes and having respective secondary emissionsurfaces in position be be impinged successively by said flat electronbeam as the beam is narrowed and undergoes deflection in the directionof said row under the influence of said deflecting electrodes, each tabbeing electrically connected to one end of a respective one of aplurality of image control grids arranged in a common plane withouttouching each other and lying perpendicular to said row, the oppositeends of said image control grids being coupled by way of resistive meansto a common terminal; and, d. a duplication of (a), (b) and (c) whereinthe common planes of the two pluralities of image control grids areadjacent and parallel, with said pluralities being mutuallyperpendicular to form a matrix of image control grids, said matrix beingadapted to be disposed in non-contacting relationship to and betweentransparent photoluminescent and photoemissive plane parallel surfacesequal in size to that of the image to be produced so as to control theimpingement of electrons emitted from the photoemissive surface upon thephotoluminescent surface.
 2. Apparatus according to claim 1, whereinsaid terminal collector anode is a metal bar electrically insulated fromsaid tabs and positioned to dissipate heat developed in said tabs byimpingement of the electron beam thereon.